1. Field of the Invention
The present invention relates to a matrix display device and a driving method thereof and, more specifically, to one suitable to be used in a liquid crystal display device in which picture elements are arranged in a matrix form.
2. Description of the Related Art
In recent years, the, field has seen the widespread use of matrix display devices such as a liquid crystal display device in which picture elements are arranged in a matrix form in place of a conventional CRT and the like because of the need for energy saving (reduced power consumption) and space saving (reduced size) of a display device. What have come into wide use are desktop personal computers, liquid crystal televisions and the like in which the aforementioned liquid crystal display devices are used as monitors.
For example, in the liquid crystal display device which is one of the matrix display devices, a plurality of scan lines and a plurality of data lines are arranged in a matrix form and display picture elements for displaying images are arranged at intersections of the scan lines and the data lines. In this liquid crystal display device, the scan lines and the data lines are driven such that the data lines are scanned one by one in sequence by means of the scan lines to apply a display voltage in accordance with the gradation of an image to be displayed to each display picture element through the data line. Thus, the liquid crystal display device displays a desired image by applying the display data voltage to liquid crystal corresponding to each display picture element to align the liquid crystal and controlling transmission of light of a backlight.
The conventional liquid crystal display device as described above, however, has a problem that the response speed required after the display data voltage is applied to the liquid crystal and until the liquid crystal demonstrates the alignment according thereto (responds thereto) is uneven in accordance with the gradation of pictures before and after the response, that is, display data voltages applied to the liquid crystal before and after the response as shown in FIG. 10.
FIG. 10 is a table showing an example of the response speed of the liquid crystal to a change in gradation of a picture.
In FIG. 10, gradation values of pictures before response are shown in the vertical direction, and gradation values after response, that is, gradation values of pictures to be displayed are shown in the horizontal direction. The gradation value of picture “1” shall display black and “64” shall display white. The gradation values of pictures of “16”, “32” and “48” are intermediate gradation levels between black and white, in which the picture becomes brighter (becomes closer to white) as the gradation value increases.
Further, response speeds of the liquid crystal to changes in gradation are indicated by symbols A to E in respective boxes at intersections of gradation values of pictures before and after response. The symbols A to E show that the response speeds become lower in an order from A, B, C, D to E, in which the symbol A is the highest response speed and the symbol E is the lowest response speed.
In FIG. 10, for example, in the case where the gradation value of a picture before response is “1” and the gradation value of a picture after response is “32”, the response speed of the liquid crystal is the lowest (symbol E). Meanwhile, in the case of the gradation value of a picture after response of “64”, the response speed of the liquid crystal is the highest (symbol A) regardless of the gradation value of a picture before response.
Because of unevenness in response speed of the liquid crystal depending on the gradation of pictures before and after response, an afterimage is caused by the unevenness in response speed of the liquid crystal when videos are displayed in the conventional liquid crystal display device, which presents a problem that pictures can not be viewed clearly.
As a method for suppressing the afterimage caused by the unevenness in response speed of the liquid crystal, there is a method of ON-OFF controlling the backlight of the liquid crystal display device during display to light the backlight like pulses by driving the backlight as a CRT so as to suppress the afterimage visible to an observer. By the aforesaid method, however, high effects can not be obtained for suppressing the afterimage visible to the observer because the response speed of the liquid crystal itself of the liquid crystal display device is very low to some change in gradation.